The present invention relates to a circuit breaker directed for a wiring circuit breaker or motor breaker for starting and stopping a motor or providing protection from overcurrent and, in particular, to an assembly structure of a main body case of a circuit breaker.
First, a circuit breaker for a three-phase circuit including main circuit contact shoes based on two-contacts bridging type is taken as an example, and the assembly structure of a conventional example thereof is shown in FIG. 5. In this figure, reference numeral 1 denotes a main-body case formed of a resin molding that is divided into three parts including a lower case 1a, an upper cover 1b, and an intermediate case 1c; reference numeral 2 denotes a power supply side main circuit terminal corresponding to each phase; reference numeral 3 denotes a load side main circuit terminal; reference numeral 4 denotes one of the fixed contact shoes connected to a conductor of the main circuit terminal 2; reference numeral 5 denotes the other fixed contact shoe; reference numeral 6 denotes a movable contact shoe for bridging the fixed contact shoes 4 and 5; reference numeral 7 denotes a movable contact shoe holder; reference numeral 7a denotes a contact spring; reference numeral 8 denotes a cage for guiding and supporting the movable contact shoe holder 7 in the opening and closing directions; reference numeral 9 denotes an arc-extinguishing plate; reference numeral 10 denotes an opening and closing lever for driving the movable contact shoe 6; reference numeral 11 denotes a toggle type contact shoe opening and closing mechanism including an opening and closing lever 10; reference numeral 12 denotes a manual operation handle; reference numeral 13 denotes an overcurrent trip device comprising a combination of a solenoid trip device 13a that operates instantaneously in response to a short circuit current or the like and a bimetal type thermal trip device 13b that performs a time limit operation in response to an overload current, the overcurrent trip device 13 being interposed and connected in series between the fixed contact shoe 5 and the load side main circuit terminal 3. An activation piece 13c of the overcurrent trip device 13 links with the contact-shoe opening and closing mechanism 11 via a trip cross bar and a latch receiver.
The lower case 1a of the main-body case 1 has contact shoe mechanisms and arc extinguishing plates for each phase in the lateral direction, and interphase partition walls or barriers molded integrally with the case so as to insulate and isolate the phases. The upper cover 1b also has interphase partition walls formed integrally at the front and rear ends thereof so as to insulate and isolate the main circuit terminals 2 for each phase. Furthermore, the main body case is assembled by mounting the opening and closing mechanisms 11 and the overcurrent trip devices 13 in the intermediate case 1c, and fitting the intermediate case 1c onto the lower case 1a. 
The operation of this circuit breaker is well known. When the operation handle 12 is placed in the ON position, the opening and closing lever 10 recedes, and the movable contact shoe 6 is urged by the contact spring 7a so as to elevate with the holder 7. The movable contact shoe 6 then comes in contact with the fixed contact shoes 4, 5 to close the circuit. In this closed circuit state, a main circuit current flows from the power supply side main circuit terminal 2 through the fixed contact shoe 4, the movable contact shoe 6, the fixed contact shoe 5, and the overcurrent trip device 13, in that order, to the load side main circuit terminal 3. Alternatively, when the operation handle 12 is moved in the opposite direction to be placed in the OFF position, the contact shoe opening and closing mechanism 11 drives the opening and closing lever 10 clockwise to push the movable contact shoe holder 7 downward. This causes the movable contact shoe 6 to be separated from the fixed contact shoes 4, 5 so as to open the main circuit contacts. On the other hand, when an overload current or a short circuit current flows through the main circuit, the overcurrent trip device 13 operates to release the latch of the contact shoe opening and closing mechanism 10, whereby the opening and closing lever 10 drives the movable contact shoe 6 in the opening direction so as to cut off the main-circuit current.
The main body case 1 of the circuit breaker, which is constructed by assembling the lower case 1a, the upper cover 1b, and the intermediate case 1c as described above, must be assembled easily, must be sufficiently rigid to accommodate a robot-based automatic assembly method, and must also have an assembly structure that can maintain an interphase insulation proof, specified in the regulations, between the main-circuit terminals for each phase.
The above-described conventional body case 1, however, has an assembly structure obtained by assembling the above-described parts in each of the lower case 1a, the upper cover 1b, and the intermediate case 1c; placing the parts at the upper cover 1b and the intermediate case 1c on the lower case 1a; and fastening them together using screws. In addition, each divided case includes no positioning or holding means for assembling with other divided case in a predetermined assembled position. Thus, a positioning operation for sequentially placing the intermediate case 1c and the upper cover 1b on the lower case 1a in the assembly process is cumbersome, and before being fastened together by using the screws, the divided cases, which overlap one another, may shift during transfer between the assembly steps. Alternatively, if there is a dimensional error or assembly error in the divided cases, a gap is created between the end surface of the interphase partition wall and the corresponding part that overlaps the end surface when the main body case is assembled. Thus, the required creepage distance of the insulation is not obtained between the main-circuit terminals for each phase.
The present invention has been made in view of the above points, and it is an object thereof to solve these problems in order to provide a rigid circuit breaker that can be assembled easily and that has an improved main body case assembly structure so as to allow the main circuit terminals for the respective phases to be sufficiently insulated.
To attain the above-described objects, the present invention provides a circuit breaker comprising main circuit terminals, fixed and movable contact shoes, arc extinguishing sections, contact shoe opening and closing mechanisms, and overcurrent trip devices for the respective phases integrated into a main-body case that constitutes a resin molding. The main body case comprises a lower case containing the contact shoes and the arc extinguishing sections for the respective phases, an intermediate case fitted on the lower case and containing power supply and load side main circuit terminal lead-out sections at the front and rear ends of the case, the contact shoe opening and closing mechanisms and the overcurrent trip devices for the respective phases, and an upper cover covering the intermediate case. The lower case and the upper cover have interphase partition walls formed integrally therewith so as to separate the phases. The intermediate case has pocket shaped sockets formed on a top-surface side thereof, in which the tips of the interphase partition walls of the upper cover are fitted when the main-body case is assembled, and the intermediate case also has recessed groove sections formed on a bottom-surface side thereof that fit over the upper edges of the interphase partition walls provided in the lower case. The embodiments are formed as follows.
(1) The main body case is assembled by assembling the upper cover and the lower case so that they surround the intermediate case, and by allowing the side walls of the upper cover to abut vertically against the end surfaces of the side walls of the lower case.
(2) The interphase partition walls formed in the upper cover and the sockets formed in the intermediate case project outward from the front and rear end surfaces of the main-body case.
With the above-described structure, when the intermediate case is fitted onto the lower case in a circuit-breaker assembly process, the upper edges of the interphase partition walls of the lower case are fitted into the recessed grooves formed on the bottom surface side of the intermediate case so that the lower case is held in its assembled position. When the upper cover is subsequently installed on the intermediate cover, the tips of the interphase partition walls of the upper cover are fitted into the sockets formed on the top surface side of the intermediate case so as to be held in position. Consequently, the divided cases can be positioned easily in the assembly process, and when they are stacked one another, the interphase partition walls of the lower case and upper cover are fitted into the grooves of the intermediate case so that the lower case and the upper cover are held in their assembly positions. As a result, the main body case becomes more rigid and is prevented from shifting from its assembled position during transfer between assembly steps. In addition, the interphase partition walls have tips that overlap the corresponding parts, that is, the sockets and recessed grooves of the intermediate case, so that a small dimensional error can be absorbed to maintain the required creepage distance of the insulation between the main circuit terminals for each phase, thereby achieving improved insulation.